Fluid-cushion sealing device

ABSTRACT

The fluid-cushion sealing device (100) for a piston (101) moving in a cylinder (102) and defining with the latter a chamber to be sealed (104) includes: a continuous perforated ring (105) through the radial thickness of which passes a calibrated opening (111) and which is sealingly accommodated in a ring groove (109) provided in the piston (101) so as to define, with said groove (109), a pressure distribution chamber (119) connected to a pressurized fluid source (112), while an axially blind counter-pressure recess (115) is provided recessed on an external cylindrical ring surface (107) which faces the cylinder (102) and which the continuous perforated ring (105) comprises, the calibrated opening (111) leading into said recess (115).

The present invention relates to a fluid-cushion sealing device.

Numerous technologies exist for producing a seal between a piston and acylinder so as to prevent a pressurized gas from leaking between saidpiston and said cylinder.

Few pistons work without sealing segment, ring or device, since theabsence of such devices leads to considerable leakage flows. In mostcases it is therefore necessary to provide a sealing device for saidpistons.

A distinction is made between sealing devices for pistons that workwithout oil which are referred to as “dry” and those that are designedto operate lubricated by oil inserted between the segment(s) or thering(s) that constitute said devices, and the cylinder with which theycooperate.

The design of a sealing device for a piston results from a compromisebetween the degree of sealing that said device procures, the energy lossdue to friction that it causes, and its useful life.

One distinguishes mainly two fields of use of sealing devices foralternating piston: compressors and motors.

The dry-air compressors are commonly used, since many applications donot tolerate any lubricant in the compressed air that they use. Thepistons which equip the dry-air compressors are mainly equipped withsealing rings made of “Teflon,” which is the trademark deposited by theAmerican company “Dupont de Nemours” for polytetrafluoroethylene, alsocalled “PTFE.” This polymer is heat stable, it has a high degree ofchemical inertness and a high anti-adhesive power. However, PTFE has thedisadvantage of a friction coefficient that is clearly higher than thatof a cut-off segment whose lubrication is ensured in the hydrodynamicregime over most of its travel. To give the polymer an acceptableresistance to abrasion and an acceptable useful life, it is possible touse a filler in the PTFE, which consists of hard grains and solidanti-friction grains such as, for example, ceramic or coke. In spite ofthese improvements, the lubricated cut-off segments that are made ofcast iron or steel generally have a better durability than the devicesmade of PTFE.

In the field of alternating internal combustion heat engines, the ringsmade of PTFE with filler are rarely used, since it is possible tolubricate the cylinder of said engines with oil without detrimentaleffect on the operation of the latter. Consequently, it is preferable toopt for lubricated cut-off segments made of cast iron that generate lessenergy losses due to friction and that have a better durability than therings made of PTFE.

Depending on the application, a selection thus has to be made between asealing ring which operates dry but which generates high losses due tofriction and is less durable, and a metal cut-off segment lubricatedwith oil, which dissipates less energy due to friction, and whose usefullife is longer. In practice, and in most cases, only the need to keepair dry and oil-free justifies the selection of a sealing ring thatoperates dry.

One also notes that, besides the need to keep the compressed air or thegas free of any presence of lubricant, some high-temperatureapplications are not compatible with lubrication itself. Indeed, beyonda certain temperature, the oil becomes cokefied and loses itslubricating properties in contact with the internal wall of thecompressor and, in particular, its cylinder and/or its segments. Thelimit coking temperature of conventional mineral oils is between onehundred sixty and two hundred degrees Celsius. The synthetic oils thathave the best performance in terms of this criterion have a limit cokingtemperature of approximately three hundred degrees Celsius, in the bestcase.

If the temperature reached during operation is even higher—for example,on the order of four hundred fifty to five hundred degrees Celsius—thereis a risk of self-ignition of the oil contained in the air as occurs indiesel engines.

However, it would be advantageous to be able to produce heat enginesequipped with a pressure-release cylinder, a cylinder head and a pistoncrown that work at even higher temperatures, on the order of a thousanddegrees Celsius and more. In this case, a Brayton cycle regenerativeengine conventionally implemented with compressors and centrifugalturbines could be implemented using volumetric piston machines. Theyield of such an engine can be significantly higher than that of theconventional alternating internal combustion heat engines with Otto orBeau de Rochas cycle controlled ignition, or diesel cycle compressionignition.

However, in such a context, the lubrication of a piston segment of aconventional internal combustion engine is impossible, since no oil canresist the mentioned temperatures on the order of a thousand degreesCelsius or more without burning or cokefying instantly. Therefore, it isnot possible to use a cut-off segment made of cast iron or steel, sincesaid segment needs to be lubricated to operate. Similarly, it isimpossible to provide a PTFE segment or similar segment whose meltingpoint is at a temperature on the order of only three hundred thirtydegrees Celsius.

In addition to the high operating temperatures, it would also beadvantageous to be able to design, produce and market non-lubricatedpiston compressors that produce dry air and whose energy loss due tofriction at the site of their piston sealing device is limited, incontrast to what a conventional PTFE ring allows.

It is for the purpose of pushing back the limits of the sealing devices,in particular for pistons of compressors and alternating engines, thatthe fluid-cushion sealing device according to the invention allows anoperation that:

-   -   has a particularly tight seal;    -   requires no lubrication;    -   generates minimal losses due to friction;    -   is compatible with a piston and/or cylinder heated to very high        temperature, on the order of a thousand degrees Celsius and        more;    -   does not come in contact with the cylinder and as a result is        robust and durable.

One notes that the field of application of the fluid-cushion sealingdevice according to the invention can extend to any other linear and/oralternating machine and, in particular, to any gas jack, pressureamplifier or pressure accumulator, these examples being given on anon-limiting basis and, in general, to any apparatus whose energyperformance and/or efficiency can be improved by said device or whosefield of application can be extended by said device.

In most applications, the fluid-cushion sealing device according to theinvention is intended to provide a gas-tight seal. However, in someapplications, said device can be used to provide a liquid-tight seal andthus become a fluid-cushion sealing device operating in the same mannerand producing the same results. Sealing off a liquid by means of afluid-cushion sealing device according to the invention can be of realadvantage, for example, for certain piston pumps that are usedparticularly in industry.

The other features of the present invention are described in thedescription and in the secondary claims which are directly or indirectlydependent on the main claim.

The fluid-cushion sealing device according to the present invention isdesigned for a piston that can move in longitudinal translation in acylinder and in the same axis as the latter, said piston and saidcylinder defining, with at least one cylinder head, a chamber to besealed, said sealing device including:

-   -   at least one continuous perforated ring which comprises an        internal cylindrical ring surface, an external cylindrical ring        surface, and two axial ring surfaces, said ring being        accommodated in at least one ring groove provided in the piston        or in the cylinder, while said ring is capable of moving        radially in the ring groove without being able to leave the        latter;    -   ring sealing means that produce a seal between each axial ring        surface and the ring groove, so that the latter defines, with        the continuous perforated ring, a pressure distribution chamber        connected by a transfer circuit to a pressurized fluid source;    -   at least one calibrated opening which passes right through the        continuous perforated ring in its radial thickness;    -   at least one fluid-cushion carrying surface which the continuous        perforated ring comprises, said carrying surface being arranged        on the opposite side from the pressure distribution chamber.

The fluid-cushion sealing device according to the present inventionincludes an axially blind counter-pressure recess provided recessed onthe external cylindrical ring surface in the case in which the ringgroove is provided in the piston, so that the surface that is notoccupied by the counter-pressure recess of the external cylindrical ringsurface which receives said recess constitutes the fluid-cushioncarrying surface.

The fluid-cushion sealing device according to the present inventionincludes an axially blind counter-pressure recess provided recessed onthe internal cylindrical ring surface in the case in which the ringgroove is provided in the cylinder, so that the surface that is notoccupied by the counter-pressure recess of the internal cylindrical ringsurface which receives said recess constitutes the fluid-cushioncarrying surface.

The fluid-cushion sealing device according to the present inventionincludes a counter-pressure recess which consists of a counter-pressuregroove of small depth more or less centered on the axial length of theexternal cylindrical ring surface or of the internal cylindrical ringsurface which receives said recess, said counter-pressure groove beingproduced over the entire circumference of said external cylindrical ringsurface or of said internal cylindrical ring surface.

The fluid-cushion sealing ring according to the present inventionincludes a calibrated opening which opens into the counter-pressurerecess.

The fluid-cushion sealing device according to the present inventionincludes a calibrated opening which opens into the counter-pressurerecess via a pressure distribution recess provided recessed at thebottom of said counter-pressure recess.

The fluid-cushion sealing device according to the present inventionincludes a pressure distribution recess, which consists of a pressuredistribution groove more or less centered on the axial length of theexternal cylindrical ring surface or of the internal cylindrical ringsurface which receives the counter-pressure recess, said pressuredistribution groove being produced over the entire circumference of saidexternal cylindrical ring surface or of said internal cylindrical ringsurface.

The fluid-cushion sealing device according to the present inventionincludes at least one of the two axial edges of the external cylindricalring surface or of the internal cylindrical ring surface on which thecounter-pressure recess is provided, which ends in an edge platingclearance.

The fluid-cushion sealing device according to the present inventionincludes ring sealing means which consist of a ring sealing lip which issecured to the continuous perforated ring, on the one hand, and whichestablishes a sealed contact with the interior or the rim of the ringgroove, on the other hand.

The fluid-cushion sealing device according to the present inventionincludes ring sealing means which consist of a thinned axial portionprovided in the vicinity of at least one of the axial ends of thecontinuous perforated ring, said portion being sealingly secured to thering groove and sufficiently flexible to allow the diameter of thecontinuous perforated ring to increase or decrease relative to that ofsaid groove.

The fluid-cushion sealing device according to the present inventionincludes a continuous perforated ring which consists of a flexiblematerial and which includes at least one circumferential ring springwhich tends to reduce the diameter of said ring if the ring groove isprovided in the piston or which tends to increase the diameter of saidring if the ring groove is provided in the cylinder.

The fluid-cushion sealing device according to the present inventionincludes a pressure distribution chamber which accommodates ring fluiddispersion means which force the ring fluid originating from thepressure transfer circuit to sweep the largest possible area of theinternal cylindrical ring surface in the case in which the ring grooveis provided in the piston or the largest possible area of the externalcylindrical ring surface in the case in which the ring groove isprovided in the cylinder, before escaping through the calibratedopening.

The fluid-cushion sealing device according to the present inventionincludes ring fluid dispersion means which consist of a dispersion plateaccommodated at the bottom of the ring groove, at least one of the axialends of said plate being provided with at least one lateral dispersionplate opening or groove which forces the ring fluid originating from thepressure transfer circuit to lead into the pressure distribution chamberthrough least one of its axial ends.

The fluid-cushion sealing device according to the present inventionincludes a ring groove which has a radial ring abutment which limits thepenetration of the continuous perforated ring into said groove.

If the ring groove is provided in the piston, the fluid-cushion sealingdevice according to the present invention includes a pressure transfercircuit which consists of a pressure intake tube parallel to thecylinder and secured to the piston, a first end of said tube leadinginto the interior of said piston while the second end of said tubeopens, via a pressure chamber borehole in which it can move bytranslation longitudinally and sealingly, into a pressure chamberconnected to the pressurized fluid source.

The fluid-cushion sealing device according to the present inventionincludes a pressure intake tube which is connected to the pressuredistribution chamber by at least one radial pressure intake duct.

The fluid-cushion sealing device according to the present inventionincludes a pressure chamber which is connected to the pressurized fluidsource by a proportional pressure non-return valve which allows the ringfluid to go from said source to said chamber but not from said chamberto said source.

The fluid-cushion sealing device according to the present inventionincludes a ring groove which accommodates an expanding spring whichbears against said groove in order to exert a radial force on theinternal ring cylindrical surface in the case in which the ring grooveis provided in the piston or on the external cylindrical ring surface inthe case in which the ring groove is provided in the cylinder.

The fluid-cushion sealing device according to the present inventionincludes an expanding spring which produces by contact a seal betweenthe ring groove and the continuous perforated ring.

The fluid-cushion sealing device according to the present inventionincludes an expanding spring which is provided with at least one fluiddispersion opening and/or with at least one fluid dispersion groove soas to constitute, with said opening and/or said groove, the ring fluiddispersion means.

The description below in reference to the appended drawings given onlyas non-limiting examples will make it possible to better understand theinvention, its features, and the advantages that it is capable ofprocuring:

FIG. 1 is a diagrammatic cross-sectional view of the fluid-cushionsealing device according to the invention, the ring sealing meansconsisting of an O-ring seal.

FIG. 2 is a diagrammatic cross-sectional view of the fluid-cushionsealing device according to the invention, the ring groove having aradial ring abutment which limits the penetration of the continuousperforated ring into said groove, while said ring consists of a flexiblematerial and includes a circumferential ring spring.

FIGS. 3 and 4 are a diagrammatic cross section and an explodedthree-dimensional view, respectively, of the fluid-cushion sealingdevice according to the invention, the ring groove accommodating anexpanding spring which produces by contact a seal between the ringgroove and the continuous perforated ring, said spring being moreoverprovided with fluid dispersion openings in order to constitute ringfluid dispersion means.

FIGS. 5 and 6 are a diagrammatic cross section and an explodedthree-dimensional view, respectively, of the fluid-cushion sealingdevice according to the invention, a dispersion plate provided withlateral dispersion plate grooves being accommodated at the bottom of thering groove, while a ring sealing lip secured to the continuousperforated ring constitutes the ring sealing means, and the continuousperforated ring comprises edge plating clearances.

FIGS. 7 and 8 are a diagrammatic cross section and an explodedthree-dimensional view, respectively, of the fluid-cushion sealingdevice according to the invention, the ring groove accommodating anexpanding ring provided with fluid dispersion openings and with fluiddispersion grooves in order to constitute the ring fluid dispersionmeans, while the ring sealing means consist of thinned axial portionsprovided in the vicinity of the axial ends of the continuous perforatedring.

FIGS. 9 and 10 are diagrammatic cross-sectional views that illustratethe operation of the fluid-cushion sealing device according to theinvention, the ring sealing means consisting of an O-ring seal.

FIG. 11 is a three-dimensional view with cutaway of a portion of aregenerative heat engine whose piston is provided with the fluid-cushionsealing device according to the invention.

FIG. 12 is an exploded three-dimensional view of a portion of aregenerative heat engine whose piston is equipped with the fluid-cushionsealing device according to the invention.

DESCRIPTION OF THE INVENTION

FIGS. 1 to 12 show a fluid-cushion sealing device 100 wherein the fluidcan be air or a liquid, various details of its components, its variants,and its accessories.

The fluid-cushion sealing device 100 according to the invention isdesigned for a piston 101 which can move by longitudinal translation ina cylinder 102 and in the same axis as the latter, said piston 101 andsaid cylinder 102 defining, with at least one cylinder head 103, achamber to be sealed 104.

As FIGS. 1 to 12 show, the fluid-cushion sealing device 100 according tothe invention includes at least one continuous perforated ring 105 whichcomprises an internal cylindrical ring surface 106, an externalcylindrical ring surface 107 and two axial ring surfaces 108.

The ring 105 is accommodated in at least one ring groove 109 provided inthe piston 101 or in the cylinder 102, while said ring 105 can moveradially in the ring groove 109 without being able to leave the latter.

One notes that if the ring groove 109 is provided in the cylinder 102,the piston 101 is a plunger piston.

One observes that in all the cases, the ring groove 109 directly orindirectly keeps the continuous perforated ring 105 axially secured tothe piston 101, if said groove 109 is provided in the piston 101, oraxially secured to the cylinder 102, if said groove 109 is provided inthe cylinder 102.

Particularly in FIGS. 1 to 10, one sees that the fluid-cushion sealingdevice 100 according to the invention includes ring sealing means 110which produce a seal between each axial ring surface 108 and the ringgroove 109, so that the latter defines, with the continuous perforatedring 105, a pressure distribution chamber 119 connected by a transfercircuit 114 to a pressurized fluid source 112.

One will also note that the ring sealing means 110 can consist of anO-ring seal 132, a lip seal, a composite seal, or any other seal orsealing segment that in itself is known regardless of what the materialor geometry may be.

It should also be noted that the internal cylindrical ring surface 106or the external cylindrical ring surface 107 facing the ring groove 109can be a non-cylindrical rotationally symmetrical shape, so that anythickness variations of the continuous perforated ring 105 are possibleover its axial length, said ring 105 possibly being either a simplecircular metal sheet deformed by burnishing or stamping, or a partproduced by rolling, using any cutting or grinding tool, or any otherelectrochemical or other production method known to the person skilledin the art.

FIGS. 1 to 10 enable one to observe that the fluid-cushion sealingdevice 100 according to the invention includes at least one calibratedopening 111 which passes right through the continuous perforated ring105 in its radial thickness. One notes that the first end of the opening111 opens on the internal cylindrical ring surface 106, while the secondend of said opening 111 opens on the external cylindrical ring surface107.

In FIGS. 1 to 3, 5, 7 and 9 to 11 one also sees that the fluid-cushionsealing device 100 according to the invention includes at least onepressurized fluid source 112 from which a pressurized ring fluid 113exits, the outlet of said fluid source 112 being connected to thepressure distribution chamber 119 by a pressure transfer circuit 114 sothat the ring fluid 113 exerts a pressure on either the internalcylindrical ring surface 106, if the ring groove 109 is provided in thepiston, or on the external cylindrical ring surface 107, if said ringgroove 109 is produced in the cylinder 102.

One notes that the ring fluid 113 can equally be a gas or a liquid andthat the pressure to which it is subjected is always greater than thepressure prevailing in the chamber to be sealed 104. As a consequence ofthe above, the diameter of the continuous perforated ring 105 increasesunder the action of the pressure of the ring fluid 113 due to theresilience of said ring 105 so that the external cylindrical ringsurface 107 tends to approach the cylinder 102 if the ring groove 109 isprovided in the piston 101, or the diameter of the continuous perforatedring 105 decreases due to the combined effect of its resilience and ofthe pressure of the ring fluid 113 so that the internal cylindrical ringsurface 106 tends to approach the piston 101 if the ring groove 109 isprovided in the cylinder 102.

One also notes that the diameter of the calibrated opening 111 iscalculated so that, taking into consideration the flow rate of the ringfluid 113 originating from the pressurized fluid source 112, thepressure that said ring fluid 113 exerts—depending on the case, on theinternal cylindrical ring surface 106 or on the external cylindricalring surface 107—always remains greater than that prevailing in thechamber to be sealed 104.

One sees that the pressurized fluid source 112 can be a piston, vane,screw, or centrifugal pneumatic fluid compressor 120 or any other typeof pneumatic fluid compressor known to the person skilled in the art, ora piston, gear, or vane type hydraulic pump or any other type ofhydraulic pump known in itself. The pneumatic fluid compressor 120,which can be a hydraulic pump, may or may not cooperate with a pressureaccumulator which in itself is known. It should be noted that a finemesh ring fluid filter 138 can be mounted upstream or downstream of thepneumatic fluid compressor 120 so as to remove from the ring fluid 113all particles exceeding a certain size before said fluid 113 isintroduced into the pressure distribution chamber 119.

FIGS. 1 to 10 show that the fluid-cushion sealing device 100 accordingto the invention includes a continuous perforated ring 105 comprising atleast one fluid-cushion carrying surface 116 arranged on the oppositeside from the pressure distribution chamber 119.

The fluid-cushion sealing device 100 includes an axially blindcounter-pressure recess 115 provided recessed on the externalcylindrical ring surface 107 in the case in which the ring groove 106 isprovided in the piston 101, so that the surface that is not occupied bythe counter-pressure recess 115 of the external cylindrical ring surface107 which receives said recess 115 constitutes the fluid-cushioncarrying surface 116.

According to a variant, the fluid-cushion sealing device 100 can includean axially blind counter-pressure recess 115 provided recessed on theinternal cylindrical ring surface 107 in the case where the ring grooveis provided in the cylinder 102, so that the surface that is notoccupied by the counter-pressure recess 115 of the internal cylindricalring surface 106 which receives said recess 115 constitutes thefluid-cushion carrying surface 116.

One notes that the extent of the counter-pressure recess 115 can be ofany dimension from the smallest, that is to say equivalent to thenon-zero radius of the mouth of the calibrated opening 111, to thelargest, that is to say just perceivably less than that of the externalcylindrical ring surface 107 or of the internal cylindrical ring surface106 which receives said recess 115. It is specified that the piston 101can comprise in the vicinity of the ring groove 109 a decompressiongroove or slots or any other internal channel or channel with a surfaceof any type whatsoever that connects said vicinity to the chamber to besealed 104.

In an embodiment variant of the fluid-cushion sealing device 100according to the invention shown in FIGS. 1 to 10, the counter-pressurerecess 115 can consist of a counter-pressure groove 117 of small depthmore or less centered on the axial length of the external cylindricalring surface 107 or of the internal cylindrical ring surface 106 whichreceives said recess 115, said counter-pressure groove 117 beingproduced over the entire circumference of said external cylindrical ringsurface 107 or of said internal cylindrical ring surface 106, theannular surfaces that border said counter-pressure groove 117constituting each a fluid-cushion carrying surface 116.

In another variant, shown in FIGS. 3 to 10, the calibrated opening 111can lead into the counter-pressure recess 115 via a pressuredistribution recess 125 provided recessed at the bottom of saidcounter-pressure recess 115.

FIGS. 3 to 10 moreover show that the pressure distribution recess 125can consist of a pressure distribution groove 126 more or less centeredon the axial length of the external cylindrical ring surface 107 or ofthe internal cylindrical ring surface 106 which receives thecounter-pressure recess 115, said pressure distribution groove 126 beingproduced over the entire circumference of said external cylindrical ringsurface 107 or of said internal cylindrical ring surface 106.

FIGS. 5 and 6 show, in addition, that at least one of the two axialedges of the external cylindrical ring surface 107 or of the internalcylindrical ring surface 106 which receives the counter-pressure recess115 can end with an edge plating clearance 118 which allows the pressureof the ring fluid 113 which the pressure distribution chamber 119contains to exert a locally higher force on the fluid-cushion carryingsurface 116 which is juxtaposed to said edge plating clearance 118.

FIGS. 5 and 6 also show that the ring sealing means 110 can consist of aring sealing lip 121 which is secured to the continuous perforated ring105, on the one hand, and which establishes a sealing contact with theinterior or the rim of the ring groove 109, on the other hand, whereinsaid sealing lip 121 can be can mounted as an added piece on thecontinuous perforated ring 105 or produced from the same piece ofmaterial as said ring 105. One notes that, alternatively, the ringsealing lip 121 can be secured to the ring groove 109, on the one hand,and establish a sealing contact with the continuous perforated ring 105,on the other hand. In this case, said lip 121 can either be mounted asan added piece on the ring groove 109 or on the rim of the latter, or itcan be made from the same piece of material as said groove 109.

Another embodiment variant of the fluid-cushion sealing device 100according to the invention is shown in FIGS. 7 and 8 according to whichthe ring sealing means 110 can consist of a thinned axial portion 139provided in the vicinity of at least one of the axial ends of thecontinuous perforated ring 105, said portion 139 being sealingly securedto the ring groove 109 and sufficiently flexible to allow the diameterof the continuous perforated ring 105 to increase or decrease relativeto that of said groove 109. One notes that the thinned axial portion 139is designed so that the material which constitutes it in no case risksyielding either due to the effect of the pressure of the ring fluid 113or due to a repeated stress that is incompatible with the fatigueresistance limits of said material.

As for FIG. 2, it shows that the continuous perforated ring 105 canconsist of a flexible material and include at least one circumferentialring spring 123 which tends to reduce the diameter of said ring 105 ifthe ring groove 106 is produced in the piston 101, or which tends toincrease the diameter of said ring 105 if the ring groove 106 isproduced in the cylinder 102. One notes that said flexible material canbe an elastomer or a polymer which may or may not have a filler ofanti-abrasive or anti-friction particles, while the circumferential ringspring 123 can be included in said material or held on the surface ofthe latter by means of a groove, a housing or abutments. Thecircumferential ring spring 123 can be helical like valve rod sealingsprings, can be a slit device, or can be of any other type capable offulfilling the desired function.

From FIGS. 3 to 8, one learns that the pressure distribution chamber 119can accommodate ring fluid dispersion means 124 which force the ringfluid 113 originating from the pressure transfer circuit 114 to sweepthe largest possible area of the internal cylindrical ring surface 106in the case in which the ring groove 106 is provided in the piston 101or the largest possible area of the external cylindrical ring surface107 in the case in which the ring groove 106 is provided in the cylinder102, before escaping through the calibrated opening 111. Thisarrangement allows the ring fluid 113 to cool the continuous perforatedring 105, the latter giving up some of its heat to the fluid 113.

Another variant shown in FIGS. 5 and 6 of the fluid-cushion sealingdevice 100 according to the invention consists in that the ring fluiddispersion means 124 can consist of a dispersion plate 136 accommodatedat the bottom of the ring groove 106, at least one of said axial ends ofsaid plate 136 being provided with at least one lateral distributionplate opening or groove 137 which forces the ring fluid 113 originatingfrom the pressure transfer circuit 114 to flow into the pressuredistribution chamber 119 by at least one of its axial ends.

In FIG. 2, one also sees that the ring groove 109 can have a radial ringabutment 127 which limits the penetration of the continuous perforatedring 105 into said groove 109, said abutment 127 possibly being—in anon-limiting manner—a cylindrical surface constituting the bottom of thering groove 109, or at least one circular ridge or raised parts arrangedat the bottom of said groove 109, or at least one chamfer or rimprovided on at least one of the two edges of said groove 109.

FIGS. 11 and 12 moreover show that, if the ring groove 109 is providedin the piston 101, the pressure transfer circuit 114 can consist of apressure intake tube 128 parallel to the cylinder 102 and secured to thepiston 101, a first end of said tube 128 leading into the interior ofsaid piston 101, while the second end of said tube 128 leads, via apressure chamber borehole 130 in which it can move by translationlongitudinally and sealingly, into a pressure chamber 129 connected tothe pressurized fluid source 112. One notes that the second end of thepressure intake tube 128 which moves by translation in the pressurechamber borehole 130 can comprise a seal which slides in said borehole130 to produce a seal. Alternatively, the pressure chamber borehole 130can comprise a seal which slides around said second end of the pressureintake tube 128 to produce a seal.

FIG. 11 shows that the pressure intake tube 128 can be connected to thepressure distribution chamber 119 by at least one radial pressure intakeduct 131 which can be produced in the mass of the piston 101 or whichcan be added to the latter, for example, by a plating of tubes which mayor may not comprise sealing gaskets and/or expanding joints.

One will also note that the pressure chamber 129 can be connected to thepressurized fluid source 112 via a proportional pressure non-returnvalve which allows the ring fluid 113 to go from said source 112 to saidchamber 129 but not from said chamber 129 to said source 112. Thisparticular arrangement makes it possible to use the variation of thevolume of the pressure chamber 129 which the back-and-forth movements ofthe second end of the pressure intake tube 128 produce in order toincrease the pressure that prevails in the pressure distribution chamber119 when the piston 101 is in the vicinity of its top dead center.

In another embodiment variant of the fluid-cushion sealing device 100according to the invention, FIGS. 3, 4, 7, 8 and 12 illustrate that thering groove 109 can accommodate an expanding spring 133 which bearsagainst said groove 109 in order to exert a radial force on the internalcylindrical ring surface 106 in the case in which the ring groove 106 isprovided in the piston 101, or on the external cylindrical ring surface107 in the case in which the ring groove 106 is provided in the cylinder102, said spring 133 possibly being a helical spring, a leaf spring, awave spring or a spring of a type known to the person skilled in theart.

One notes, particularly in FIGS. 3, 4, 7 and 8, that the expandingspring 133 can produce by contact a seal between the ring groove 109 andthe continuous perforated ring 105.

Said figures also show that the expanding spring 133 can be providedwith at least one fluid dispersion opening 134 and/or with at least onefluid dispersion groove 135 so as to form, with said opening 134 and/orsaid groove 135, the ring fluid dispersion means 124.

OPERATION OF THE INVENTION

The operation of the fluid-cushion sealing device 100 according to theinvention is understandable in view of FIGS. 9 and 10 which show, inparticular, ring sealing means 110 consisting of an O-ring seal 132.

According to the non-limiting embodiment example of the sealing device100 shown in FIGS. 9 and 10, the ring groove 109 is provided in thepiston 101 and not in the cylinder 102. Consequently, the pressuredistribution chamber 119 is located on the 106 side of the internalcylindrical ring surface.

One notes that in said FIGS. 9 and 10 symbols “+” and “−” enclosed by acircle have been added, illustrating the difference between the pressureprevailing in the pressure distribution chamber 119, on the one hand,and the pressure prevailing in the pressure distribution groove 126, thecounter-pressure groove 117, and the chamber to be sealed 104, on theother hand.

We will assume that the maximum pressure prevailing in the chamber to besealed 104 is twenty bars, while the pressurized fluid source 112produces a flow of ring fluid 113 whose maximum pressure is forty bars.

FIG. 9 shows the fluid-cushion sealing device 100 according to theinvention, when the pressurized fluid source 112 is just starting todeliver ring fluid 113 and the pressure distribution chamber 119 is juststarting to increase in pressure. We will assume that at this stage thepressure prevailing in the chamber to be sealed 104 is still only oneabsolute bar.

One observes that the pressure distribution chamber 119 having beensealed, in particular by means of the O-ring 132, the ring fluid 113 hasno exit other than through the calibrated opening 111 to escape fromsaid chamber 119. In the operating stage of the fluid-cushion sealingdevice 100 according to the invention illustrated in FIG. 9, the fullflow of ring fluid 113 originating from the pressurized fluid source 112has not yet been established, so that the pressure prevailing in thepressure distribution chamber 119 is only ten bars.

In spite of the fact that the pressure of forty bars has not yet beengenerated by the pressurized fluid source 112, one observes that thecontinuous perforated ring 105 is starting to expand in spite of theescape of ring fluid 113 through the calibrated opening 111, since thepressure prevailing in the pressure distribution chamber 119 is higherthan the pressure prevailing in the pressure distribution groove 126,the counter-pressure groove 117, and the chamber to be sealed 104.

The expanding of the continuous perforated ring 105 is symbolized by thedotted-line arrow. The flow of ring fluid 113 which escapes through thecalibrated opening 111 joins with the chamber to be sealed 104 via thepressure distribution groove 126, the counter-pressure groove, and theinterstice formed by the clearance left between the piston 101 and thecylinder 102, respectively.

One will also note that the cross section of the calibrated opening 111and the flow of ring fluid 113 generated by the pressurized fluid source112 are calculated so that the pressure of forty bars—when it has indeedbeen generated by said source 112—can be maintained in the pressuredistribution chamber 119, in spite of the ring fluid 113 escapingthrough the calibrated opening 111. This is equivalent to saying that,if no obstacle limits the expanding of the continuous perforated ring105, the latter receives enough flow of ring fluid 113 from thepressurized fluid source 112 to expand as much as it would if it wereperfectly sealed, that is to say as much as it would if it did not havea calibrated opening 111.

As for the radial thickness of the continuous perforated ring 105, it iscalculated so that—taking into account the resilience of the materialconstituting said ring 105—, when a pressure of forty bars is applied tothe internal cylindrical ring surface 106, the external diameter of thecontinuous perforated ring 105 is at least equal to and even greaterthan the internal diameter of the cylinder 102.

With the pressure rising gradually in the pressure distribution chamber119, the diameter of the continuous perforated ring 105 increases untilthe fluid-cushion carrying surfaces 116 are a very short distance fromthe wall of the cylinder 102. This is what is represented in FIG. 10.

At this operating stage of the fluid-cushion sealing device 100according to the invention, a significant pressure loss is createdbetween the fluid-cushion carrying surfaces 116 and the cylinder 102,said loss opposing the passage of the ring fluid 113. Consequently, thepressure that prevails in the pressure distribution groove 126 and thecounter-pressure groove 117 increases to the point of being close to thepressure prevailing in the pressure distribution chamber 119. From thisit results that the pressure prevailing in said chamber 119 no longerexerts a radial force on the continuous perforated ring 105 except atthe fluid-cushion carrying surfaces 116. Consecutively to this, due tothe resilience conferred to it by the properties of a spring, whichmakes it resistant to expanding, the continuous perforated ring 105retracts, which has the effect, on the one hand, of reducing the loadloss between the fluid-cushion carrying surfaces 116 and the cylinder102, and, on the other hand, of lowering the pressure prevailing in thepressure distribution groove 126 and the counter-pressure groove 117,which again causes the continuous perforated ring 105 to expand.

As can be observed, the constrictive force resulting from the stiffnessof the continuous perforated ring 105, which opposes the expanding ofthe latter, on the one hand, and the load loss created between thefluid-cushion carrying surface 116 and the cylinder 102, on the otherhand, lead to a relatively unstable situation of the continuousperforated ring 105. Indeed, when the diameter of said ring 105increases, the conditions that led to said increase in diameterdisappear, while, when the diameter of said ring 105 decreases, theconditions that lead to said increase are again all present.

From this it results that the fluid-cushion carrying surfaces 116 haveno choice but to find a relatively stable intermediate position at avery short distance from the cylinder 102. Said distance results fromthe initial clearance between the piston 101 and the cylinder 102, fromthe pressure that prevails in the pressure distribution chamber 119,from the stiffness of the continuous perforated ring 105, and from thetotal axial length of the fluid-cushion carrying surfaces 116 relativeto the total axial length of the internal cylindrical ring surface 106which is exposed to the pressure of the ring fluid 113. Said distancealso results from the depth of the counter-pressure groove 117, whichitself represents an additional load loss.

According to the operating example considered here, once the pressure offorty bars is established in the pressure distribution chamber 119, thedistance between the fluid-cushion carrying surfaces 116 and thecylinder 102 is on the order of either several microns or on the orderof one micron or even a fraction of a micron. It is this short distancewhich, combined with a flow of ring fluid 113 that always goes from thecounter-pressure recess 115 towards the chamber to be sealed 104 and notin the opposite direction, produces a very tight seal between the piston101 and the cylinder 102.

One observes that, taking into consideration the particular operatingmode of the fluid-cushion sealing device 100 according to the invention,the continuous perforated ring 105 naturally tends to become centered inthe cylinder 102 and to adjust for any defects in circularity orcylindricity of said cylinder 102. Indeed, the position of thecontinuous perforated ring 105 results from an equilibrium between,first, the general constrictive force of said ring 105 given by thestiffness of the latter and, second, the local radial forces applied ateach point of the periphery and of the axial length of the continuousperforated ring 105, said forces resulting from the aerodynamicinteraction between the fluid-cushion carrying surfaces 116 and thecylinder 102.

One also notes that the design of the fluid-cushion sealing device 100according to the invention leaves numerous possibilities for adaptationto each application. For example, all things being equal otherwise, thecross section of the calibrated opening 111 makes it possible toregulate the distance left between the fluid-cushion carrying surfaces116 and the cylinder 102, said distance being possibly also regulated bythe stiffness of the continuous perforated ring 105 which depends, inparticular, on its thickness.

It is easy to conclude from the operation that has just been describedthat it is absolutely necessary that the pressure generated by thepressurized fluid source 112 is always greater than that prevailing inthe chamber to be sealed 104. This does not rule out thepossibility—over sufficiently long time scales—to adapt the pressuregenerated by the pressurized fluid source 112 to the maximum pressureoccurring in the chamber to be sealed 104. However, one notes that, ifthe pressure chamber 129 has a proportional pressure non-return valve,the pressure that prevails in the pressure distribution chamber 119 canvary over short time scales like the pressure prevailing in the chamberto be sealed 104. This strategy can be retained, for example, if theapplication in which the fluid-cushion sealing device 100 according tothe invention is used is a pneumatic compressor.

Thus, one sees that the fluid-cushion sealing device 100 according tothe invention provides access to new possibilities that are notaccessible to conventional sealing devices for pistons.

In particular, it becomes possible to design a regenerative engine bymeans of volumetric piston machines whose general principle andorganization is similar to those of Brayton cycle regenerative enginescommonly implemented by means of compressors and centrifugal turbines.One will also note that said regenerative engine is very different fromengines having compressors and centrifugal turbines both in terms of itsembodiment as well as in terms of innovations that it uses so that it isboth producible and efficient. Such a piston regenerative enginerequires that the operating temperature of the cylinder 102 and of thepiston 101 be on the order of a thousand degrees Celsius and more. Atsuch a temperature, the use of any lubrication by oil whether of asegment or of a ring is ruled out. Moreover, whatever the material usedis to produce said cylinder 102 and said piston 101, for example, aceramic based on alumina, zirconium or silicon carbide or any othermaterial, at such a temperature, any contact between said cylinder 102and a sealing segment or gasket is impossible.

However, the fluid-cushion sealing device 100 according to the inventionis compatible with such operating conditions. Indeed, the continuousperforated ring 105 never comes in contact with the cylinder 102, sinceit is separated from the latter by a film of ring fluid 113 which canbe—as a non-limiting example—air of which the atmosphere is made.Moreover, the continuous perforated ring 105 is constantly cooled byflow of ring fluid 113 which passes through it and which sweeps theinternal cylindrical ring surface 106 and the external cylindrical ringsurface 107. In this regard, it must be recalled that, in order toassist this cooling, the pressure distribution chamber 119 canaccommodate ring fluid dispersion means 124 such as those shown in FIGS.3 to 8. Said cooling, in particular, makes it possible to use acontinuous perforated ring 105 made of steel having the desiredmechanical resistance, without exceeding the tempering temperature ofsaid steel which is only a few hundred degrees Celsius. The use of acontinuous perforated ring 105 made of steel heated to several hundredsof degrees in a cylinder 102 made of ceramic heated to more than athousand degrees Celsius moreover makes it possible to control theoperating clearance between said ring 105 and said cylinder 102 undergood conditions, which is easily demonstrated by calculation. This isdue, in particular, to the expanding coefficient of steel which ishigher than that of the ceramic whether or not said steel is coated witha protective layer that protects it against oxidation.

One also notes that the cooling of the continuous perforated ring 105has, as a corollary, the local heating of the ring fluid 113, whichmakes it possible to increase the volume of said fluid 113. Thisadvantageously makes it possible to reduce the flow of ring fluid 113produced by the pressurized fluid source 112, while at the same timeallowing the extensible continuous fluid-cushion sealing device 100according to the invention to operate under the desired conditions. Onealso notes that it is possible to regulate the temperature of the ringfluid 113 before introducing it into the pressure chamber 129, whichmakes it possible to regulate the operating temperature of thecontinuous perforated ring 105 and thus the operating clearance betweensaid ring 105 and the cylinder 102.

One also observes that the flow of ring fluid 113 which flows betweenthe fluid-cushion carrying surfaces 116 and the cylinder 102 ensures thecontinual cleaning of the latter. Thus, solid particles and residues ofany type cannot adhere to the cylinder 102. In addition, it is notpossible for a particle originating from the chamber to be sealed 104 topass between the fluid-cushion carrying surfaces 116 and the cylinder102, since the pressure of the gases in said chamber 104 is lower thanthe pressure prevailing in the pressure distribution chamber 119. Onewill also note that, in order to guarantee an optimal operation of thefluid-cushion carrying surfaces 116, it is possible to provide a ringfluid filter 138 which removes any particle whose diameter is, forexample, greater than one micron from the ring fluid 113 before saidfluid 113 is introduced into the pressure distribution chamber 119.

As a consequence of what has just been said, the fluid-cushion sealingdevice 100 according to the invention makes it possible, in particular,to produce a high-yield regenerative heat engine whose cylinder 102which is exposed to high temperatures is shown in FIGS. 11 and 12. Oneobserves in said figures that said heat engine comprises, in particular,two cylinder heads 103 and a piston 101 connected to a power outputshaft 17 by mechanical transmission means 18. The piston 101, thecylinder 102 and the cylinder heads 103 define two chambers to be sealed104 each of which can be put in connection either with a hot gas intakeduct 19 by intake metering valves 24 or with a low-pressure gas exhaustduct 26 by exhaust valves 31.

In FIGS. 11 and 12, one notes the presence of the pressure intake tube128 oriented parallel to the cylinder 102 and secured to the piston 101,a first end of said tube 128 leading to the interior of the piston 101,while the second end of said tube 128 leads, via the pressure chamberborehole 130 in which it can move by translation longitudinally andsealingly, into the pressure chamber 129 which is connected to thepressurized fluid source 112 by the pressure transfer circuit 114. Onealso observes—particularly in FIG. 11—that the pressure intake tube 128is connected to the pressure distribution chamber 119 by a radialpressure intake duct 131 added in the piston 101.

The possibilities of the fluid-cushion sealing device 100 according tothe invention are not limited to the applications that have just beendescribed, and moreover it must be understood that the above descriptionwas given only as an example and that it in no way limits the scope ofsaid invention which one would not exceed by replacing the details ofexecution described by any other equivalent.

1. A fluid-cushion sealing device for a piston, wherein: said sealingdevice is configured to move in longitudinal translation in a cylinder,along an axis of the cylinder, said piston and said cylinder defining,with at least one cylinder head, a chamber to be sealed, wherein thesealing device comprises: at least one continuous perforated ring whichcomprises an internal cylindrical ring surface, an external cylindricalring surface, and two axial ring surfaces, said ring being configured tobe accommodated in at least one ring groove provided in the piston or inthe cylinder, while said ring is capable of moving radially in the ringgroove without being able to leave the ring groove, said continuousperforated ring being sufficiently flexible to allow the diameter of thecontinuous perforated ring to increase or decrease relative to saidgroove under an effect of a pressure of a source of pressurized fluid; aring seal that produces a seal between each axial ring surface and thering groove, so that the ring groove defines, with the continuousperforated ring, a pressure distribution chamber connected by a transfercircuit to a pressurized fluid source; at least one calibrated openingwhich passes right through the continuous perforated ring in its radialthickness; at least one fluid-cushion carrying surface which thecontinuous perforated ring comprises, said carrying surface beingarranged on the opposite side from the pressure distribution chamber. 2.The fluid-cushion sealing device according to claim 1, wherein the ringgroove is provided in the piston, further comprising an axially blindcounter-pressure recess provided recessed on the external cylindricalring surface, so that the surface that is not occupied by thecounter-pressure recess of the external cylindrical ring surface whichreceives said recess constitutes the fluid-cushion carrying surface. 3.The fluid-cushion sealing device according to claim 1, wherein the ringgroove is provided in the cylinder, further comprising an axially blindcounter-pressure recess provided recessed on the internal cylindricalring surface, so that the surface that is not occupied by thecounter-pressure recess of the internal cylindrical ring surface whichreceives said recess constitutes the fluid-cushion carrying surface. 4.The fluid-cushion sealing device according to claim 1, furthercomprising a counter-pressure recess that consists of a counter-pressuregroove of small depth that is approximately centered on the axial lengthof the external cylindrical ring surface or of the internal cylindricalring surface which receives said recess, said counter-pressure groovebeing produced over the entire circumference of said externalcylindrical ring surface or of said internal cylindrical ring surface.5. The fluid-cushion sealing device according to claim 3, furthercomprising a calibrated opening which opens into the counter-pressurerecess.
 6. The fluid-cushion sealing device according to claim 2,wherein t the calibrated opening opens into the counter-pressure recessvia a pressure distribution recess provided recessed at the bottom ofsaid counter-pressure recess.
 7. The fluid-cushion sealing deviceaccording to claim 6, wherein the pressure distribution recess consistsof a pressure distribution groove which is more or less centered on theaxial length of the external cylindrical ring surface or of the internalcylindrical ring surface which receives the counter-pressure recess,said pressure distribution groove being produced over the entirecircumference of said external cylindrical ring surface or of saidinternal cylindrical ring surface.
 8. The fluid-cushion sealing deviceaccording to claim 1, wherein at least one of the two axial edges of theexternal cylindrical ring surface or of the internal cylindrical ringsurface which receives the counter-pressure recess ends in an edgeplating clearance.
 9. The fluid-cushion sealing device according toclaim 1, wherein the ring seal consists of a ring sealing lip which issecured to the continuous perforated ring, on the one hand, and whichestablishes a sealed contact with the interior or the rim of the ringgroove, on the other hand.
 10. The fluid-cushion sealing deviceaccording to claim 1, wherein the ring seal consists of a thinned axialportion provided in a vicinity of at least one of the axial ends of thecontinuous perforated ring, said thinned axial portion being sealinglysecured to the ring groove and sufficiently flexible to allow thediameter of the continuous perforated ring to increase or decreaserelative to said groove.
 11. The fluid-cushion sealing device accordingto claim 1, wherein the continuous perforated ring consists of aflexible material and includes at least one circumferential ring springwhich tends to reduce the diameter of said ring if the ring groove isprovided in the piston or which tends to increase the diameter of saidring if the ring groove is provided in the cylinder.
 12. Thefluid-cushion sealing device according to claim 1, wherein the pressuredistribution chamber accommodates a ring fluid disperser which force thering fluid originating from the pressure transfer circuit to sweep thelargest possible area of the internal cylindrical ring surface in thecase in which the ring groove is provided in the piston or the largestpossible area of the external cylindrical ring surface in the case inwhich the ring groove is provided in the cylinder, before escapingthrough the calibrated opening.
 13. The fluid-cushion sealing deviceaccording to claim 12, wherein the ring fluid disperser consist of adispersion plate accommodated at the bottom of the ring groove, at leastone of the axial ends of said plate being provided with at least onelateral dispersion plate opening or groove which forces the ring fluidoriginating from the pressure transfer circuit to lead into the pressuredistribution chamber through at least one of its axial ends.
 14. Thefluid-cushion sealing device according to claim 1, wherein the ringgroove accommodates an expanding spring which bears against said groovein order to exert a radial force on the internal cylindrical ringsurface in the case in which the ring groove is provided in the pistonor on the external cylindrical ring surface in the case in which thering groove is provided in the cylinder.
 15. The fluid-cushion sealingdevice according to claim 14, wherein the expanding spring produces bycontact a seal between the ring groove and the continuous perforatedring.
 16. The fluid-cushion sealing device according to claim 14,wherein the pressure distribution chamber accommodates ring fluiddisperser which force the ring fluid originating from the pressuretransfer circuit to sweep the largest possible area of the internalcylindrical ring surface in the case in which the ring groove isprovided in the piston or the largest possible area of the externalcylindrical ring surface in the case in which the ring groove isprovided in the cylinder, before escaping through the calibratedopening, and the expanding spring is provided with at least one fluiddispersion opening and/or with at least one fluid dispersion groove soas to constitute, with said opening and/or said groove, the ring fluiddisperser.